It is well known to transfer a large quantity of heat by circulating fluid through a closed loop using a pump. JP 2003/232596, for example, discloses a heat transfer system of a forced convection type by circulating a magnetic fluid in a magnetic field. This system does not require electrical power and allows to construct in a simple structure without occupying a large space.
Developments in the technology concerning the synthesis and micronization of metal oxide-ferromagnetic materials in recent years have remarkably improved the efficiency of convectional heat transfer by the magnetic fluid.
However, the heat transfer efficiency based on the spontaneous convection has a certain limit no matter how the performance of magnetic fluid is improved. Accordingly, it is difficult to develop a magnetic element capable of transferring a large quantity of heat.
Since the efficiency of heat transfer by the convention decreases as the temperature differential decreases, a temperature differential of at least 10° C. is generally required in the working environment to transfer the heat by the spontaneous convection.